This invention is related in general to the field of control systems. More particularly, the invention is related to a gimbal pointing vector stabilization control system and method.
Stabilization is the function of holding steady the line-of-sight vector of a gimbaled sensor system subject to the motion of the vehicle to which the sensor base is attached. The line-of-sight vector or the pointing vector is the imaginary line from the aperture center of the gimbaled sensor to the target of interest. As the vehicle base of the gimbal moves or rotates, the gimbal must move equal and opposite as the body in order to remain pointing at the target. The problem is complicated by the fact that often it is impossible to mount a sensing device on the gimbal itself to measure the effects of vehicle base motion.
Feedback control is a technique that has been utilized extensively in pointing vector stabilization systems. Feedback control involves the measurement of a desired plant state with a sensor, and the comparison of this measured state with the desired command. Any plant input is driven by the error between the commanded state and the actual measured state. Feedback stabilization systems use sensing elements mounted directly to the gimbal to sense the effects of vehicle base motion. Feedforward stabilization is used when such sensors cannot be mounted to the gimbal.
Current approaches to feedforward stabilization include what is known as position feedforward and rate feedforward. Position feedforward techniques determine the angle that the body has rotated and attempts to move the gimbal an equal and opposite amount. Rate feedforward techniques determine the speed that the body is spinning and attempts to move the gimbal at an equal and opposite speed.
There are many error sources and difficult challenges that must be overcome when using these known methods. For example, some type of measuring device must be available to detect the angle that the gimbal is at and/or the speed at which it is turning. Likewise, a measuring device such as a gyroscope is mounted on the vehicle base to detect its motion. These measuring devices inevitably have scale factor errors, biases, and latencies associated with them that deteriorates the performance of the gimbal stabilization.
Accordingly, there is a need for an accurate gimbal stabilization control system and method which eliminates or substantially reduce the disadvantages associated with prior control systems.
In one aspect of the invention, a hybrid stabilization system for isolating a pointing vector of a gimbal from the motion of a vehicle base is provided. The hybrid stabilization control system includes a rate feedback loop generating a rate feedback compensation value in response to a measured rate difference between a pointing vector rate of motion and a vehicle base rate of motion, a rate feedforward loop generating a rate feedforward compensation value in response to a measured inertial vehicle base rate of motion, a position feedback loop generating a position feedback compensation value in response to a measured position difference between a pointing vector angular position and a vehicle base angular position, a position feedforward loop generating a position feedforward compensation value in response to a measured inertial vehicle base angular position. A controller receives a pointing vector position command and generates a gimbal control signal in response to the rate feedback compensation value, rate feedforward compensation value, position feedback compensation value, and position feedforward compensation value.
In another aspect of the invention, a hybrid stabilization system for isolating a pointing vector of a gimbal from the motion of a measurable disturbance is provided. The system includes a relative rate sensor measuring a rate difference between a pointing vector rate of motion and a disturbance rate of motion, and a rate feedback loop generating a rate feedback compensation value in response to the rate difference. An inertial rate sensor measuring an inertial disturbance rate of motion, and a rate feedforward loop generating a rate feedforward compensation value in response to the inertial disturbance rate are also included. The system further includes a relative angular position sensor measuring a position difference between a pointing vector angular position and a disturbance angular position, and a position feedback loop generating a position feedback compensation value in response to the position difference. An inertial angular position sensor measuring an inertial disturbance angular position and a position feedforward loop generating a position feedforward compensation value in response to the inertial disturbance angular position are included. The system also includes a controller receiving a pointing vector position command and generating a gimbal control signal in response to the rate feedback compensation value, rate feedforward compensation value, position feedback compensation value, and position feedforward compensation value.
In yet another aspect of the invention, a hybrid stabilization method for isolating a pointing vector of a gimbal from the motion of a vehicle base includes the steps of generating a rate feedback compensation value in response to a measured rate difference between a pointing vector rate of motion and a vehicle base rate of motion, generating a rate feedforward compensation value in response to a measured inertial vehicle base rate of motion, generating a position feedback compensation value in response to a measured position difference between a pointing vector angular position and a vehicle base angular position, generating a position feedforward compensation value in response to a measured inertial vehicle angular position, and receiving a pointing vector position command and generating a gimbal control signal in response to the rate feedback compensation value, rate feedforward compensation value, position feedback compensation value, and position feedforward compensation value.
In yet another aspect of the invention, the inventive steps of a hybrid stabilization method for isolating a pointing vector of a gimbal from the motion of a vehicle base include measuring a rate difference between a pointing vector rate of motion and a vehicle base rate of motion, generating a rate feedback compensation value in response to the rate difference, measuring an inertial vehicle base rate of motion, generating a rate feedforward compensation value in response to the inertial vehicle base rate, measuring a position difference between a pointing vector angular position and a vehicle base angular position, generating a position feedback compensation value in response to the position difference, measuring an inertial vehicle base angular position, generating a position feedforward compensation value in response to the inertial vehicle angular position, and receiving a pointing vector position command and generating a gimbal control signal in response to the rate feedback compensation value, rate feedforward compensation value, position feedback compensation value, and position feedforward compensation value.